1. Field of the Invention
The present disclosure relates to a wireless power transmission system for wirelessly and contactlessly transmitting power using resonant magnetic coupling. The present disclosure also relates to a wireless power transmitting apparatus and a wireless power receiving apparatus which are used in the wireless power transmission system, and relates to control circuits of the wireless power transmitting apparatus and the wireless power receiving apparatus.
2. Description of Related Art
U.S. Patent Application Publication No. 2008/0278264 (FIGS. 12 and 14) discloses a wireless power transmission apparatus for transmitting energy through space between two resonant circuits. The wireless power transmission apparatus wirelessly (contactlessly) transmits oscillating energy by coupling two resonant circuits through leakage of oscillating energy at a resonance frequency (evanescent tail) generated in space around the resonant circuits.
If a metal foreign object is present near a coil of a power transmitting resonant circuit or a coil of a power receiving resonant circuit during power transmission of a wireless power transmission system, an eddy current may be generated on the metal foreign object, resulting in heating of the metal foreign object. In order to safely use the wireless power transmission system, it is necessary to suppress heating of the metal foreign object.
For example, a noncontact power transmission system disclosed in Japanese Patent No. 4743173 stops power transmission upon detecting a metal foreign object, thus suppressing heating of the metal foreign object.
However, in a wireless power transmission system that stops power transmission whenever detecting a metal foreign object, the wireless power transmission system cannot resume power transmission unless a user removes the metal foreign object. In order to improve the usability of the wireless power transmission system, it is desirable that, when a metal foreign object is detected, the wireless power transmission system be able to continue power transmission while suppressing heating of the metal foreign object.